1. Field of the Invention
The present invention relates to an encoder, in which as a rotary member is rotated, a state between A-channel and C-channel and a state between B-channel and C-channel switch between a conductive state and a nonconductive state, and more particularly, relates to an encoder, in which even if small-sized, a pattern of electrode can be easily formed for A-channel, B-channel and C-channel.
2. Description of the Related Art
FIG. 8 is an explanatory drawing showing a summary of a construction of a conventional rotary encoder, and FIG. 9 shows wave-form charts (A) and (B) of output from the encoder. For example, an encoder of this kind is disclosed in Japanese Patent No. 2506877.
Conductive sliders 102, 103 and 104 are provided opposite a surface of a disk-shaped substrate 100. On the surface of the substrate 100, a disk-shaped electrode 105, which is formed of a conductive material such as gold, silver and copper, is disposed. The sliders 102, 103 and 104 come into contact with the electrode 105 at three different positions aligned radially of the substrate 100.
In the electrode 105, an inner peripheral region 106 with which the G-channel slider 102 as a common slider comes into contact is formed continuously all round in a rotating direction. An intermediate region 107 with which the H-channel slider 103 comes into contact is formed such that conductive portions 107a and nonconductive portions 107b alternate with each other in the rotating direction. Likewise, an outer peripheral region 108 with which the I-channel slider 104 comes into contact is formed such that conductive portions 108a and nonconductive portions 108b alternate with each other in the rotating direction. The conductive portions 107a and nonconductive portions 107b in the intermediate region 107 are offset by only a slight angle in the rotating direction from the conductive portions 108a and nonconductive portions 108b in the outer peripheral region 108.
The nonconductive portions 107b and 108b are formed by removing part of the electrode 105 to expose a nonconductive surface of the substrate 100.
(A) of FIG. 9 shows a waveform for ON/OFF switching between the H-channel and the G-channel and a waveform for ON/OFF switching between the I-channel and the G-channel when the substrate 100 is rotated in a CW (clockwise) direction relative to the sliders 102, 103 and 104. On the other hand, (B) of FIG. 9 shows a waveform for ON/OFF switching between the H-channel and G-channel and a waveform for ON/OFF switching between the I-channel and G-channel when the substrate 100 is rotated in a CCW (counterclockwise) direction relative to the sliders 102, 103 and 104.
As the substrate 100 is rotated, the state between the H-channel and the G-channel switches between ON and OFF. When the state between the H-channel and the G-channel switches from OFF to ON and back to OFF, the value of count information in a detection circuit is counted up by “1” (in the CW direction) or counted down by “1” (in the CCW direction).
Moreover, since a phase shift Tδ is provided between ON/OFF cycle between the H-channel and the G-channel and ON/OFF cycle between I-channel and the G-channel, the rotating direction of the substrate 100 can be identified. If the state between the H-channel and the G-channel is switched to ON but the state between the I-channel and the G-channel remains unchanged from OFF after the state between the H-channel and the G-channel and the state between the I-channel and the G-channel are both OFF, the rotating direction is CW; if the state between the H-channel and the G-channel remains unchanged from OFF but the state between the I-channel and the G-channel is switched to ON after the state between the H-channel and the G-channel and the state between the I-channel and the G-channel are both OFF, the rotating direction is CCW.
In an encoder of this kind, furthermore, a click mechanism is provided between the substrate 100 and a housing which is a fixed side. For example, an outer peripheral surface of the substrate 100 is repeatedly recessed in the rotating direction and the housing is provided with a plate spring for fitting in the recesses. Accordingly, the position of the substrate 100 can be stabilized each time the substrate 100 is rotated by a predetermined angle.
In the invention disclosed in Japanese Patent No. 2506877, the substrate 100 is stabilized when the H-channel slider 103 comes into contact with the nonconductive portion 107b and the I-channel slider 104 comes into contact with the nonconductive portion 108b, i.e., at respective phases CKa, CKb, CKc, etc., as shown in FIG. 8. Japanese Patent No. 2506877 discloses that since the H-channel slider 103 and the I-channel slider 104 are electrically disconnected from each other at the time when the substrate 100 is stabilized, malfunction in circuit can be prevented.
In the conventional encoder shown in FIGS. 8 and 9, the state between the H-channel and the G-channel switches from OFF to ON and back to OFF during rotation for one click angle due to the click mechanism, e.g., during rotation from the stable position CKa to the stable position CKb, and the value of count information in the detection circuit is counted up or down by “1” at each rotation for one click operation. That is, one conductive portion 107a and one nonconductive portion 107b for one cycle portion are present within a rotation angle θ for one count up or one count down; one conductive portion 108a and one nonconductive portion 108b for one cycle portion are also present within the rotation angle θ.
Accordingly, if the diameter of the substrate 100 is decreased to produce a small-sized encoder, the area of the substrate 100 within the angle θ is extremely decreased, so that one conductive portion 107a and one nonconductive portion 107b for one cycle portion and one conductive portion 108a and one nonconductive portion 108b for one cycle portion need be disposed within such a small area. Therefore, the pattern of the electrode 105 need be precisely processed, which results in the necessity of providing a high-cost production process such as precise etching or laser processing.
In the conventional encoder which identifies the rotating direction with the phase shift Tδ provided between ON/OFF cycle between the H-channel and the G-channel and ON/OFF cycle between I-channel and the G-channel, moreover, the phase shift Tδ need be extremely small so as to switch the state between I-channel and the G-channel from ON to OFF without fail at the stable positions CKa, CKb, etc. However, if the phase shift Tδ is so small and the diameter of the substrate 100 is decreased, the dimension in the rotating direction corresponding to the phase shift Tδ becomes extremely small.
Therefore, the rotating direction of the rotary member may be erroneously detected once a slight scratch is made on the electrode 105 by sliding contact with the sliders. Such erroneous detection of the rotating direction of the rotary member may also be caused by chattering noises produced when the slider 103 passes over the boundary between the conductive portion 107a and nonconductive portion 107b and when the slider 104 passes over the boundary between the conductive portion 108a and nonconductive portion 108b. 